In recent years, there has been a demand for the effective utilization of low-quality fuels such as coal or heavy oil from the perspective of diversification so as to actively use low-quality fossil fuels in addition to high-quality fossil fuels. In addition, integrated coal gasification combined cycle (IGCC), in which gas turbines using gas fuel and steam turbines are used in combination, and power generation by means of introducing hydrocarbon gas into fuel cells are also becoming widespread from the perspective of improving power generation efficiency in the field of thermal power generation. Therefore, there is research and development underway to gasify low-quality fuels and use them for such power generation.
Incidentally, a low-quality fuel typically contains a large amount of sulfur compounds, and when a gas obtained by gasifying, this fuel is combusted directly, the sulfur compounds are discharged from the chimney into the atmosphere as sulfur oxides, which become a source of environmental pollution such as acid rain. Therefore, in ordinary thermal power generation, a method of installing an exhaust gas desulfurizer on the downstream side of the boiler so as to remove sulfur compounds as gypsum, for example, has been put into practical application. However, in combined cycle power generation the inlet temperature of a gas turbine is higher than the boiler temperature in ordinary thermal power generation, so the corrosion of the material is substantial. Therefore, it is necessary to protect the material by removing various impurities such as sulfur compounds on the upstream side rather than the downstream side of the gas turbine. For example, when installing a fuel cell power generator, it is essential to secure power generation efficiency and durability by protecting the material, and various impurities must be similarly removed on the upstream side of the fuel cell.
A so-called wet gas purification process, wherein water-soluble components are removed with a water scrubber and hydrogen sulfide (H2S) is removed with an aqueous amine solution, has been put into practical application as such a method for removing impurities. However, although hydrogen sulfide (H2S) can be removed with an aqueous amine solution, carbonyl sulfide (COS) cannot be removed. Therefore, a hydrolysis reaction expressed by formula (1) is performed using a COS hydrolysis catalyst so as to accelerate a reaction for converting the substance into the form of hydrogen sulfide (H2S) which can be removed with an aqueous amine solution.COS+H2O→H2S+CO2  (1)
Here, examples of known COS hydrolysis catalysts include catalysts containing titania, catalysts containing alumina, a group IV metal and barium, and catalysts containing an alkali metal, chromium oxide, and alumina (Patent Document 1).
Incidentally, in integrated coal gasification combined cycle (IGCC), there is a problem in that when a COS hydrolysis catalyst is used continuously for COS in a gasified gas, so-called catalyst poisoning occurs, wherein the dust content (for example, sulfides) in the gasified gas covers the surface of the COS hydrolysis catalyst, which causes a decrease in catalyst performance.
The catalyst with reduced performance as a result of poisoning is reused by means of regeneration treatment.
A method of performing heat treatment on as catalyst and then re-supporting sodium carbonate, for example, has been proposed as such a catalyst regeneration method (Patent Document 2).